The present invention relates to capacitive fuses for missiles.
In previously known capacitive fuses the sensitivity obtainable has been severely limited by interference from sources such as corona discharge of the self capacitance of the missile body, which body becomes charged during passage of the missile through the atmosphere, from vibration of the missile body and from movements of the missile control surfaces.
It is an object of the present invention to provide a capacitive fuse in which the effects of such interference are reduced.
According to a first aspect of the present invention in a capacitive fuse for a missile there are provided a source of alternating current signals a transmitter electrode, two receiver electrodes and means to derive a signal dependent upon the difference between alternating signal currents received from said transmitter electrode by said receiver electrodes, the size and disposition of said receiver electrodes being arranged substantially to minimise interference in said difference current.
According to a second aspect of the present invention in a capacitive fuse for a missile comprising a source of alternating current signals, a transmitter and one or more receiver electrodes and means responsive to components of said alternating current signals passing byway of said transmitter and receiver electrodes, a phase sensitive detector is arranged to derive the signal passed to said means in dependence upon the signal currents flowing into said one or more receiver electrodes whereby the effective level of components not synchronous with said alternating current signal is reduced.
According to a third aspect of the present invention in a capacitive fuse for a missile comprising a source of alternating current signals, a transmitter and one or more receiver electrodes and means responsive to components of said alternating current signals received at said receiver electrodes, there is provided control means to apply alternating current signals from said source to said first mentioned means substantially in antiphase to alternating current signals from said source reaching said first mentioned means by capacitive coupling between said transmitter and receiver electrodes, whereby the effects of unwanted components in the signals from said source may be substantially reduced at the input to said first mentioned means.
Preferably the control means is such that the amplitude of alternating current signals passed by said control means to the input of said first mentioned means is at least partially dependent upon an output signal from said first-mentioned means.
According to a fourth aspect of the present invention in a capacitive fuse for a missile there are provided a source of alternating current signals, a transmitter electrode, at least two differing receiver electrode assemblies, and means to compare signals received by way of said two receiver electrode assemblies and to provide an output substantially only when the signals received by way of the two receiver electrode assemblies are of predetermined relative amplitudes.
Preferably said receiver electrode assemblies comprise respectively one and two receiver electrodes.